1. Field of the Invention
The present invention relates to a semiconductor memory device, and more particularly, the present invention relates to a nonvolatile memory device, an operating method thereof, and a memory system including the same.
2. Description of the Related Art
Semiconductor memory devices are storage devices that store data and output the stored data as needed. Semiconductor memory devices may be characterized as either volatile memory devices or nonvolatile memory devices. A volatile memory device is a memory device which loses its stored data when power to the device is cut off. Examples of volatile memory devices include SRAM, DRAM, SDRAM, and the like. A nonvolatile memory device is a memory device which retains its stored data even in the event that power to the device is cut-off. Examples of nonvolatile memory devices include ROM, PROM, EPROM, EEPROM, flash memory device, PRAM, MRAM, RRAM, FRAM, and the like. In general, a flash memory device can be characterized as either being a NOR type or a NAND type.
A nonvolatile memory device includes a plurality of nonvolatile memory cells. Repetitive program/erase operations of the nonvolatile memory device eventually cause deterioration of nonvolatile memory cells, thus changing its operating properties. As operating properties and reliability of nonvolatile memory devices are lowered due to deterioration of the nonvolatile memory cells, operating speed of the nonvolatile memory devices may also be lowered. Thus, an object of the invention is to secure read margin, prevent read errors and improve operating speed of a nonvolatile memory device.